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On her regular walk to the research facility, scientist Miriam San José stoops near a small pond surrounded by thick vegetation and retrieves a small plastic sound device.

She had placed there overnight to capture the distinctive calls of the Scinax quinquefasciatus, known by local scientists as an invasive species with effects that experts are just beginning to understand.

Although abounding with unique wildlife – including centuries-old giant tortoises, swimming iguanas, and the well-known finches that sparked Charles Darwin's theory of evolution – the island chain near the shoreline of Ecuador had historically been free of amphibians.

In the late 1990s, this shifted. Several small amphibians traveled from continental the mainland to the archipelago, likely as hitchhikers on transport vessels.

Genetic studies suggest that, through time, there have been multiple unintentional introductions to the archipelago, and the amphibians now have a strong foothold on two locations: Isabela and Santa Cruz.

The population is expanding so rapidly that scientists have been struggling to monitor, estimating populations in the millions on each island, across developed and farming areas, but also in the protected Galápagos national park.

When the biologist marked amphibians and attempted to recapture them in the following 10 days, she could find only a single tagged frog from time to time, indicating their numbers were enormous.

They calculated 6,000 frogs in a solitary pond. "The calculations are still very conservative," says San José. "I'm quite certain there are additional numbers."

Deafening Noise and Rising Worries

The frogs' abundance is clear from the sound disruption they cause. "The amount of frogs and the sound – it's truly incredible," says San José.

For the researchers, their nocturnal vocalizations are useful in estimating their presence in remote areas, using recorders like the one near the office.

But nearby agricultural workers say the sounds are so loud they prevent sleep at night.

"During the wet season, I constantly hear their calls and they're really loud," says Jadira Larrea Saltos from Santa Cruz.

"Initially it was a surprise, seeing the initial frogs in the region," says Larrea Saltos, who started noticing their abundance about three years ago when one leaped on her hand as she was stepping out of her house.

Ecological Impact Stays Unknown

The noise isn't the fundamental problem, though. While the species has been in the islands for nearly 30 years, experts still know very little about its impact on the islands' precariously balanced land and water ecosystems.

On islands, it is very common for invasive species to prosper, as they have few of their enemies. The islands has over sixteen hundred introduced species, many of which are significantly disrupting the safety of its native ones.

A 2020 study suggests the invasive amphibians are hungry insect consumers, and might be unevenly consuming uncommon bugs found exclusively on the archipelago, or depleting the nutrition of the islands' rare birds, disrupting the ecosystem balance.

Unique Characteristics and Management Difficulties

The island amphibians have shown some unusual traits, including surviving in slightly salty water, which is rare for frogs.

Their metamorphosis stage is also extremely variable, with some larvae turning into frogs very quickly and others taking a long time: San José witnessed one which remained as a tadpole in her lab for six months.

"We truly don't know this aspect," she says, worried the tadpoles could be affecting the region's clean water, a very scarce resource in the islands.

Methods to curb the frogs in the early 2000s were mostly ineffective. Conservation officers tried collecting large numbers by manual methods and gradually raising the salt content of lagoons in without success.

Research suggests spraying caffeine – which is extremely poisonous to frogs – or using electrical methods could help, but these approaches aren't necessarily safe for other uncommon Galápagos organisms.

Lacking solutions to more of the fundamental issues about their lifestyle and effect, removing the frogs might not even be the right way to proceed, says the biologist.

Financial Obstacles for Study

While she hopes the increasing use of eDNA methods and DNA analysis will help her group understand of the invader, financial support for the research has been difficult to come by.

"Everybody wants to give funding for preserving frogs," says San José. "But it's more difficult to find financial backing for an invasive frog that you might want to manage."